DEV: Switch off of our image_optim fork (#13124)

The main image_optim gem now includes the timeout feature
that we had in our fork. So it is now safe to switch off of our fork and
back to the image_optim gem.

This is the link to the commit in the image_optim repo that adds the
timeout option:

ec3767dde0

One difference with the new timeout implementation is that image_optim
now handles the timeout exceptions instead of bubbling them up:

1ed0328587/lib/image_optim.rb (L128-L129)

```
 rescue Errors::TimeoutExceeded
   handler.result
```

So a timeout will just return `nil`, which is the same response if it
couldn't optimize an image. I don't think we were really watching for
or doing anything about these timeout warnings in our logs so I think
this is an okay change to have and we will have less warnings in our
logs now too.

lib/upload_creator.rb

@@ -424,8 +424,6 @@ class UploadCreator
     OptimizedImage.ensure_safe_paths!(@file.path)
     FileHelper.optimize_image!(@file.path)
     extract_image_info!
-  rescue ImageOptim::TimeoutExceeded
-    Rails.logger.warn("ImageOptim timed out while optimizing #{@filename}")
   end
 
   def filesize